1. Field of the Invention
The present invention relates to a method for detecting even hidden faults within integrated circuit modules by reducing the internal noise margin and to a circuit arrangement for accomplishing same.
2. Description of the Prior Art
In large scale integrated (LSI) circuit modules, there is no direct external access to internal circuit parts, such as for testing. While functional checking of the circuitry is possible, it is generally not possible to perform noise immunity testing of the internal circuit parts. As such, internal circuit parts which have a diminished noise immunity due to technological deficiencies are not discovered by circuit testing since the tests cannot be carried out under the sort of "worst case" conditions which can occur during use of the circuit.
German Patent No. OS 30 40 733 discloses a method for investigating integrated circuits which includes exposing portions of the circuit which generally have a low noise immunity to the influence of alpha radiation so as to further reduce the noise immunity. The resulting misbehavior, or malfunction, of the circuit is observed. The disclosed method is especially useful for memory circuit modules. It is, however, rather involved and, therefore, useful only during the development phase of circuit production. For example, it is used to investigate the initial production run of a circuit type.
Reference voltage generators as found in integrated circuits are known, for example, from Tagungsbericht ESSCIRC, 22-24 Sept. 1981, pp. 205-207, and from German Patent No. 28 49 153.